X-ray CT apparatuses have an X-ray source and an X-ray detector arranged facing each other with an object therebetween. The X-ray detector includes a plurality of channels (M channels) of detection elements along a direction (a channel direction) perpendicular to a longitudinal direction of a table-top as a body axis direction.
While various types of X-ray detectors may be employed, a scintillation detector, which can be small-sized, is typically used in the X-ray CT apparatus. Each detection element of the scintillation detector has a scintillator and an optical sensor such as a PD (photodiode). The scintillator absorbs X-rays collimated at a preceding stage to thereby produce light (fluorescence). The PD converts the light into an electric signal by the optical sensor, and outputs the electric signal to a DAS. A plurality of C-amp chips and A/D conversion chips are mounted on the DAS. The C-amp chip amplifies a voltage signal based on the electric signal. The A/D conversion chip converts the amplified signal into a digital signal. In the X-ray CT apparatus, the X-ray source emits an X-ray beam in a fan shape toward a section of the object, and each detection element of the X-ray detector converts the X-ray beam transmitted through a slice surface of the object into the electric signal. Transmission data can be thereby collected.
The C-amp chip and the A/D (analog to digital) conversion chip of the DAS are electronic parts. When the chips are exposed to X-rays (radiation) for a long period of time, trouble may occur on the DAS. Thus, the DAS is arranged (mounted) at a position not exposed to X-rays in a gantry (a rotation unit) of the X-ray CT apparatus.
In recent years, high integration or high-density packaging of electronic parts has been enabled, and a technique to integrally form the X-ray detector and the DAS (as a module) has been also developed to improve performance. When the X-ray detector and the DAS are integrally formed, however, the DAS is arranged on a side opposite to an X-ray incident side across the X-ray detector, that is, at a position exposed to X-rays not fully absorbed and thus leaking from the X-ray detector. The DAS is thereby exposed to X-rays not fully absorbed and thus leaking from the X-ray detector when the X-ray detector and the DAS are integrally formed, so that trouble such as a breakdown may occur on the DAS.
When the DAS is arranged at a position not exposed to X-rays in a structure where the X-ray detector and the DAS are integrally formed, the detection element of the X-ray detector and the DAS cannot be arranged in a tiling fashion.